CN116223978A - Low-current grounding line selection method and system - Google Patents
Low-current grounding line selection method and system Download PDFInfo
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
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Abstract
The invention provides a small-current grounding line selection method and a small-current grounding line selection system, comprising the following steps: acquiring three-phase voltage of a bus and judging whether a small-current grounding fault occurs or not; if the low-current grounding fault occurs, extracting the power frequency fault quantity of the zero-mode current of the line or extracting the transient fault quantity of the zero-mode current of the line; respectively inputting the extracted line fault quantity and the small current ground fault reference quantity into a ground line selection criterion for comparison and judgment; if the fault line is the fault line, a tripping instruction is sent out; otherwise, no trip instruction is issued.
Description
Technical Field
The invention belongs to the technical field of relay protection of power systems, and particularly relates to a low-current grounding line selection method and a line selection system.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The neutral points of the power system are: grounding modes such as non-grounding, grounding through arc suppression coils, grounding through small resistors, direct grounding and the like. The neutral point is not grounded or grounded through an arc suppression coil, and the grounded power system has wide application in a power distribution system, and when a single-phase grounding fault occurs, the grounding current is relatively small, and the power system is also called a small-current grounding system. The low-current grounding system generates single-phase grounding, and a fault line needs to be selected and cut off.
The existing low-current grounding line selection methods are many, for example: patent documents with application numbers CN200410024015.8, CN201610974094.1, CN201611109129.1, CN201710796987.6, CN201811004696.X, CN201910527688.1, CN 201910595675.8. These documents have respective advantages, but also have various drawbacks, respectively.
The current practical application of the distributed small-current grounding line selection device is that the grounding line selection method is generally as follows: and (3) extracting the zero-mode voltage transient fault quantity of the bus as a reference quantity, comparing the zero-mode current transient fault quantity of the protected circuit with the zero-mode current transient fault quantity of the protected circuit, and judging whether the protected circuit is a faulty circuit or not. Because the power system has distributed capacitance, the functional relation between the bus zero-mode voltage transient state fault quantity and the protected line zero-mode current transient state fault quantity is greatly influenced by the distributed capacitance, so that the reliability of the grounding line selection criterion based on the comparison of the voltage transient state fault quantity and the current transient state fault quantity is unstable.
For example: patent document CN 202010250971.7 proposes a low-current grounding line selection method, which uses the transient fault amount extracted by the current at both sides of the transformer as a reference amount, and compares the reference amount with the zero-mode current transient fault amount of the protected line to determine whether the line is faulty. The method is based on comparison of two current transient fault quantities, is basically not influenced by the distributed capacitance of the power system, and has higher reliability in line selection criteria. However, the method is derived on the basis that the small current ground fault amount only exists on the load side of the transformer and the system thereof and cannot be transmitted to the power side of the transformer and the system thereof.
The inventors found in the study that: the small current ground fault quantity is transmitted to the transformer power supply side and the system thereof as well as the transformer load side and the system thereof. Therefore, the accuracy of the small current grounding line selection scheme according to the technical scheme corresponding to the patent document CN 202010250971.7 is questionable.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a small-current grounding line selection method, and the utilized grounding line selection criterion is not basically influenced by the distributed capacitance of the power system, so that the judgment result is little interfered and the reliability is high.
To achieve the above object, one or more embodiments of the present invention provide the following technical solutions:
in a first aspect, a low current grounding line selection method is disclosed, including:
establishing a power frequency fault reference quantity based on the three-phase current instantaneous value of the load side of the transformer;
calculating the zero sequence current of the protected line based on the zero mode current instantaneous value of the protected line;
comparing the zero sequence current of the protected line with the reference quantity of the power frequency fault, and if the protected line is the fault line, sending a tripping instruction; otherwise, no trip instruction is issued.
As a further technical scheme, comparing the zero-sequence current of the protected circuit with a power frequency fault reference, and if the power frequency fault reference is opposite to the zero-sequence current of the protected circuit, the circuit is a fault circuit; if the power frequency fault reference quantity is the same as the zero sequence current direction of the protected circuit, the circuit is a non-fault circuit.
As a further technical scheme, when the power frequency fault reference is established based on the three-phase current instantaneous value of the load side of the transformer, the negative sequence current of the fault phase of the load side of the transformer is used as the power frequency fault reference.
As a further technical scheme, a power frequency fault quantity method for making small current grounding select lines is used for a scene of an under-compensation state of a neutral point through arc suppression coil grounding system by using a criterion, wherein the criterion is as follows:
∣2I 2 ∣>∣K set I 0 i, wherein I 2 For the negative sequence component of the fault phase of the load side of the transformer, I 0 K is zero sequence current of load side of transformer set The reliability coefficient is 1-5.
In a second aspect, a low current grounding line selection method is disclosed, comprising:
establishing transient fault reference quantity based on the three-phase current transient value of the load side of the transformer;
calculating the transient state quantity of the zero-mode current of the protected line based on the transient value of the zero-mode current of the protected line;
comparing the transient quantity of the zero-mode current of the protected line with a transient fault reference quantity, and if the protected line is a fault line, sending a tripping instruction; otherwise, no trip instruction is issued.
As a further technical scheme, comparing the transient state quantity of the zero-mode current of the protected circuit with a transient state fault reference quantity, and if the waveform of the transient state fault reference quantity is similar to the waveform of the transient state quantity of the zero-mode current of the protected circuit in the opposite direction, the circuit is a fault circuit; if the waveform of the transient fault reference quantity is similar to the transient quantity of the zero-mode current of the protected line in the same direction, the line is a non-fault line.
As a further technical scheme, the step of establishing the transient fault reference quantity based on the three-phase current transient value of the load side of the transformer comprises the following steps:
adding three-phase currents at the load side of the transformer to obtain a first current;
adding the two non-fault phase currents on the load side of the transformer;
filtering transient fault quantity of current obtained by adding two non-fault phase currents;
adding the current obtained after the transient fault quantity is filtered with the fault phase current of the load side of the transformer to obtain a second current;
and subtracting the first current from the second current, wherein the difference value is the transient fault reference quantity of the fault phase.
As a further technical scheme, the step of establishing the transient fault reference quantity based on the three-phase current transient value of the load side of the transformer comprises the following steps:
step (1) obtaining the current of the same fault at the load side of the transformer;
step (2) copying the current obtained in the step (1);
filtering transient fault quantity of the current obtained by replication;
and (4) subtracting the current obtained in the step (3) from the current obtained in the step (1), wherein the difference value is the transient fault reference quantity of the fault phase.
As a further technical scheme, the step of calculating the transient state quantity of the zero-mode current of the protected line comprises the following steps:
Step (1) obtaining zero-mode current of a protected circuit;
step (2) copying the zero-mode current obtained in the step (1);
filtering the transient fault quantity of the zero-mode current obtained by replication;
and (4) subtracting the current obtained in the step (3) from the zero-mode current obtained in the step (1), wherein the difference value is the transient state quantity of the zero-mode current of the protected line.
When the zero sequence current of the protected circuit is compared with the power frequency fault reference quantity, or when the transient quantity of the zero mode current of the protected circuit is compared with the transient fault reference quantity, a one-by-one comparison mode or a simultaneous comparison mode is adopted; when adopting the mode of comparing one by one, the zero sequence currents of all the protected circuits are compared with the power frequency fault reference quantity one by one according to the sequence, and as the comparison is carried out independently, whether the protected circuits are fault circuits or not can be determined after the comparison; when a plurality of or all the protected line zero sequence currents are simultaneously compared with the power frequency fault reference quantity, identification is needed for each protected line, coding or numbering is adopted or an ID is established, the protected line zero sequence currents and the identifications of the protected lines are in one-to-one correspondence, and therefore if a certain protected line is judged to be a fault line, a specific fault line can be identified.
In a third aspect, a low-current grounding line selection system is disclosed, where the low-current grounding line selection system adopts the above-mentioned low-current grounding line selection method, and the method includes:
at least one reference quantity generating device for low-current grounding faults and at least one low-current grounding line selecting device;
all the low-current grounding line selection devices are communicated with one low-current grounding fault reference quantity generation device;
the low-current ground fault reference amount generating device is configured to: when a small-current ground fault occurs, establishing a small-current ground fault reference quantity based on a three-phase current instantaneous value at the load side of the transformer;
the low current ground line selection device is configured to: when a small-current ground fault occurs, calculating the transient quantity of the zero sequence current or zero mode current of the protected line based on the zero mode current transient value of the protected line; and comparing the transient state quantity of the zero sequence current or zero mode current of the protected circuit with the corresponding small current grounding fault reference quantity, and judging whether the circuit is a fault circuit.
In the above technical scheme, each protected line is configured with a low-current grounding line selection device, or a plurality of lines are configured with a low-current grounding line selection device, or all lines share a low-current grounding line selection device.
As a further technical scheme, the number of the small-current ground fault reference quantity generating devices is equal to the number of the small-current ground line selecting devices, or the number of the small-current ground fault reference quantity generating devices is smaller than the number of the small-current ground line selecting devices.
As a further technical scheme, the low-current ground fault reference quantity generating device sends the generated low-current ground fault reference quantity to at least one low-current ground fault line selecting device;
the small-current ground fault reference quantity generating device and the small-current ground line selecting device are equal in quantity or unequal in quantity for information interaction.
As a further technical scheme, the low-current ground fault reference quantity generating device further receives bus three-phase voltage, judges whether the low-current ground fault occurs or not based on the bus three-phase voltage, and judges the fault phase.
As a further technical solution, the device further comprises a current/voltage converter, wherein the current/voltage converter converts a three-phase current instantaneous value at the load side of the transformer into a voltage wave with a similar waveform, and the converted voltage wave is transmitted to the small-current ground fault reference quantity generating device.
As a further technical solution, the low-current ground fault reference generating device and the low-current ground line selecting device each include a current transient fault amount extracting circuit, configured to calculate a transient amount of zero-mode current of a protected line or a transient fault reference amount of a fault phase from a current transient value, where the circuit includes:
The current transformers CT1, CT2 and CT3, wherein the current transformer CT1 comprises coils L1 and L2, the current transformer CT2 comprises coils L3 and L4, and the current transformer CT3 comprises coils L5, L6 and L7;
and an inductor L8, an amplifying circuit, and a transient fault amount processing circuit;
the synonym end of the coil L1 is connected with the homonym end of the coil L2;
the homonymous end of the coil L3 is connected with the homonymous end of the coil L5, and the heteronymous end of the coil L2 is connected with the heteronymous end of the coil L5;
the homonymous end of the coil L4 is connected with the inductor L8 in series and then is connected with the homonymous end of the coil L6, and the homonymous end of the coil L4 is connected with the homonymous end of the coil L5; the two ends of the coil L6 are connected with the two input ends of the amplifying circuit, and the output end of the amplifying circuit is connected with the input end of the transient fault quantity processing circuit.
The one or more of the above technical solutions have the following beneficial effects:
according to the technical scheme, the transient fault quantity is not required to be extracted by utilizing the currents at the two sides of the transformer as the reference quantity, the ground line selection criterion is used for comparing the reference quantity of the current fault at the load side of the transformer with the zero-mode current of the protected line, and the functional relation between the two current waveforms used for comparison is basically not influenced by the distributed capacitance of the power system, so that the judgment result is less interfered and the reliability is very high.
According to the technical scheme, when the reference quantity of the current faults at the load side of the transformer is obtained, only three current parameters are needed to be obtained, and compared with a mode that six current components are needed for calculating the current extraction transient fault quantity at the two sides of the transformer, the method is smaller in operation quantity and easier and quicker to obtain the reference quantity data.
When only one small-current grounding fault reference quantity generating device in the line selection system is needed, all small-current grounding fault reference quantities needed by all small-current grounding line selection devices are transmitted through communication, the small-current grounding line selection devices are simple in integral structure and easy to meet a plurality of requirements, and therefore the line selection system is easy to realize.
When the number of the small current ground fault reference quantity generating devices in the line selection system is equal to that of the small current ground fault reference quantity generating devices, three-phase current on the load side of a transformer is adopted to flow into a current/voltage converter, and then the current/voltage converter sends voltage waves to the small current ground fault reference quantity generating devices respectively. The voltage distribution mode is convenient for wiring, and the reliability is improved.
Compared with the prior art, the line transient fault quantity extraction method of the invention is characterized in that in order to obtain the transient quantity of the zero-mode current, the current is duplicated, the transient quantity of the zero-mode current is firstly removed for one of the current, then the line transient fault quantity is obtained by subtracting the transient quantity of the zero-mode current from the original line zero-mode current, and the whole obtaining mode is simpler; the extracted transient state quantity waveform of the zero-mode current relatively completely reserves the original transient state fault quantity waveform before being extracted, and lays a good foundation for correctly judging the action criterion.
The invention uses criterion (|2I) 2 ∣>∣K set I 0 And) the power frequency fault quantity method of small current grounding line selection can be used for a part of scenes in the under-compensation state of the neutral point grounding system through the arc suppression coil, and the grounding line selection reliability of the part of scenes is improved.
Additional aspects of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.
FIG. 1 is a diagram of a neutral point ungrounded system in accordance with an embodiment of the present invention;
fig. 2 is a diagram of a neutral point through arc suppression coil grounding system according to an embodiment of the present invention.
FIG. 3 is a schematic diagram of a transient fault amount extraction circuit according to an embodiment of the present invention;
wherein: 1. an amplifying circuit, a transient fault quantity processing circuit;
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present invention.
Embodiments of the invention and features of the embodiments may be combined with each other without conflict.
Example 1
The embodiment discloses a low-current grounding line selection system, which comprises at least one low-current grounding fault reference quantity generating device and at least one low-current grounding line selection device (also called as a low-current grounding protection device). The low-current grounding line selection device can be distributed, namely: each protected line is provided with a small-current grounding line selection device, so that when one of the small-current grounding line selection devices is damaged, the protection of one line is only affected, and the damage range is small.
The low-current grounding line selection device can also adopt a centralized scheme: namely: the small current grounding line selection devices of all lines are concentrated and combined in one device, so that the use amount of the whole computer chip of the system can be reduced, and the cost is reduced.
The small-current grounding line selection device can also adopt the combination of two schemes of a distributed type and a centralized type, a plurality of small-current grounding line selection devices are used for dividing the protected lines into a plurality of groups, each group is provided with one small-current grounding line selection device, each small-current grounding line selection device is used for protecting a plurality of lines respectively, and all lines are respectively arranged to the corresponding small-current grounding line selection device of each group according to the groups. Each line is provided with a mark, and the low-current grounding line selection device is convenient to determine specific fault lines in each group.
The low-current ground fault reference amount generating device inputs the bus three-phase voltage and also inputs three-phase currents ia, ib, ic on the transformer load side of the connection bus, as shown in fig. 1 and 2. Each small current grounding line selection device of the protected line configuration inputs zero mode current (also called zero sequence current) of the protected line, for example: i shown in FIG. 1 and FIG. 2 01 、i 02 、i 03 。
Specifically, in this embodiment, all the low-current ground fault reference amount generating devices are shared by all the low-current ground fault line selecting devices, so that all the low-current ground fault line selecting devices have respective communication lines connected with the shared low-current ground fault reference amount generating devices, and the communication connection lines may be optical fibers or electric wires. The communication line establishes communication between the low-current ground fault reference quantity generating device and the low-current ground line selecting device to perform information interaction.
The low-current ground fault reference quantity generating device is used for judging whether the low-current ground fault occurs or not by using the input bus three-phase voltage and judging the fault phase, and generating the low-current ground fault reference quantity required by a ground line selection criterion by using three-phase currents ia, ib and ic of the load side of a transformer connected with the bus; the low-current ground fault reference generating device can also generate other needed information according to requirements, such as: and when the fault of the low-current grounding system occurs, information such as whether a neutral point is not grounded to the system, whether the neutral point is in a complete compensation state, whether the neutral point is in an under compensation state and an under compensation degree, whether the neutral point is in an over compensation state and an over compensation degree, and the like. The small-current ground fault reference quantity generating device can transmit related information to the small-current ground line selecting device, and all the small-current ground line selecting devices can receive the information sent by the small-current ground fault reference quantity generating device. The low-current ground fault reference generating device can also receive information sent by the low-current ground line selecting device.
The low-current ground fault reference amount generating device generates information of the low-current ground fault reference amount generating device to obtain whether the low-current ground fault occurs or not. If the small current grounding fault occurs, the small current grounding line selection device inputs the small current grounding fault reference quantity and the zero mode current of the protected line into a grounding line selection criterion for comparison and judgment, and if the small current grounding line selection device is a faulty line, a tripping instruction is sent out; otherwise, no trip instruction is issued.
The reference quantity generating device of the small current grounding fault in the embodiment only needs one reference quantity generating device of the small current grounding fault, all the reference quantities of the small current grounding fault needed by the small current grounding line selecting devices are transmitted through communication, the small current grounding line selecting devices can be designed very simply, and the manufacturing cost of the line selecting system is low due to the fact that the small current grounding line selecting devices are numerous in quantity.
Example two
The small current grounding fault reference quantity generating device is shared by all the small current grounding line selecting devices, the problem that the small current grounding fault reference quantity required by the small current grounding line selecting devices is transmitted through communication exists, and if the communication transmission line is too long, the communication reliability is reduced.
The embodiment discloses a small-current grounding line selection system, wherein the number of small-current grounding fault reference quantity generation devices is equal to that of the small-current grounding line selection devices; in this way, each low-current ground fault reference amount generating device can be assembled with one low-current ground line selecting device into a whole; the small-current grounding line selection device and the small-current grounding fault reference quantity generation device which are arranged in a whole can communicate nearby to exchange information; the communication line is very short and the reliability is very high; and parallel communication can be adopted, so that the communication speed is increased.
Wherein, a little electric current ground connection route selection device protects several circuits, and a few little electric current ground connection route selection device protects all circuits.
The low-current ground fault reference amount generating means is configured to: when a small-current ground fault occurs, a small-current ground fault reference quantity is established based on the three-phase current instantaneous value at the load side of the transformer.
The low-current ground fault reference amount generating device inputs the bus three-phase voltage and also inputs three-phase currents ia, ib, ic on the transformer load side of the connection bus, as shown in fig. 1 and 2. Each small current grounding line selection device of the protected line configuration inputs zero mode current (also called zero sequence current) of the protected line, for example: i shown in FIG. 1 and FIG. 2 01 、i 02 、i 03 。
The low-current grounding line selection device is configured to: when a small-current ground fault occurs, calculating the power frequency quantity of the zero-mode current of the protected line or the transient quantity of the zero-mode current based on the zero-mode current transient value of the protected line; and comparing the power frequency quantity of zero-mode current or the transient quantity of zero-mode current of the protected line with the corresponding small-current grounding fault reference quantity, and judging whether the protected line is a fault line or not.
In the above scheme, the number of the reference quantity generating devices for the small-current ground fault is large, each device needs to input three-phase currents ia, ib and ic, all devices need to flow three-phase currents in series, and the load of a current loop is large. In addition, the current loop of any small current ground fault reference generating device is interrupted, and the current loops of all small current ground fault reference generating devices are also interrupted at the same time.
In order to solve the above-described problem, in the present embodiment, it is possible to employ a configuration in which three-phase currents on the load side of the transformer first flow into one current/voltage converter, the current/voltage converter converts the three-phase currents into voltage waves of similar waveforms, and the voltage waves are supplied to the respective small-current ground fault reference amount generating devices, respectively. The small current grounding line selection device receives voltage waves in a parallel mode instead of a serial mode, so that the voltage wave input circuit of one small current grounding line selection device is disconnected, and the normal operation of other small current grounding line selection devices is not affected. The wiring is convenient, and the reliability is improved.
The same parts as those of the first embodiment are not redundant.
Example III
The purpose of this embodiment is to provide a small current grounding line selection method:
and judging whether the protected line is a faulty line or not by adopting a power frequency fault quantity method. The neutral point ungrounded system shown in fig. 1 is used for analysis as follows. The Ia, ib and Ic represented by the three-phase current instantaneous values at the load side of the transformer are represented as Ia, ib and Ic by phasors due to the fault analysis of the power frequency fault quantity; i represented by instantaneous value of zero-mode current of line 01 、i 02 、i 03 Represented by phasors as I 01 、I 02 、I 03 。
As shown in fig. 1, the earth fault occurs in the a phase of the L1 line, the b and c compatible currents of all the lines flow into the earth, and the capacitive currents of the non-faulty phases (b and c phases) of the lines L1, L2 and L3 flow into the earth are respectively expressed as: k (k) 1 I c 、k 2 I c 、k 3 I c The method comprises the steps of carrying out a first treatment on the surface of the Wherein: k (k) 1 、k 2 、k 3 The split coefficients of lines L1, L2, L3 are respectively: (k) 1 +k 2 +k 3 ) =1; all capacitive currents I c The fault amount of the a-phase coil on the load side of the transformer (Δia=i c ) The fault quantity delta Ib= (-0.5I) of the coils on the load side b and c of the transformer flows out through the coils on the b and c of the transformer c )、ΔIc＝(-0.5I c ) The fault currents Δib, Δic flow into the b, c phases of the busbar M and are then distributed proportionally to the b, c phases of the respective lines, i.e. the non-fault phase currents flowing into the lines L1, L2, L3, i.e.: k (k) 1 I c 、k 2 I c 、k 3 I c The method comprises the steps of carrying out a first treatment on the surface of the Forming a capacitive current I c Is a closed loop of (c).
At this time, zero sequence currents I of lines L1, L2, L3 01 ＝(-I c +k 1 I c )、I 02 ＝(k 2 I c )、I 03 ＝(k 3 I c )。
If the low-current grounding system is in a normal working state, no fault occurs, the three-phase current Ia, ib and Ic of the transformer only comprises the load current of the transformer, and the load current is positive sequence current and no negative sequence current. When the small-current grounding system fails, the three-phase current Ia, ib and Ic of the transformer not only comprises the load current of the transformer, but also comprises the fault quantity current, and the power frequency quantity in the fault quantity current is expressed as delta Ia, delta Ib and delta Ic. It is easy to see that: Δib= (-0.5Δia= -0.5I c )、ΔIc＝(-0.5ΔIa＝-0.5I c )。
An L1 line is subjected to a-phase grounding fault, and the negative sequence current of a fault phase at the load side of the transformer is as follows:
I 2 ＝(Ia+a 2 Ib+aIc)/3
＝(ΔIa+a 2 ΔIb+aΔIc)/3
＝(ΔI c +a 2 (-0.5I c )+a(-0.5I c ))/3
＝(0.5I c )
zero sequence current of load side of transformer:
I 0 ＝((ΔIa+ΔIb+ΔIc)/3)＝0
the reference quantity generating device for small current grounding faults extracts the negative sequence current I of the fault phase from ia, ib and ic 2 As a reference for power frequency faults.
The power frequency fault amount of the zero-mode current of the protected line, which is also called as the power frequency fault amount of the protected line, may also be called as the zero-sequence current of the protected line.
Analysis showed that: the power frequency fault reference quantity is opposite to the zero sequence current of the fault line; the power frequency fault reference quantity and the zero sequence current of the non-fault line are in the same direction.
Therefore, the low-current grounding line selection device can judge whether the line is faulty or not by comparing the low-current grounding line selection device with the zero-sequence current of the protected line after obtaining the power frequency fault reference quantity transmitted by the low-current grounding fault reference quantity generation device.
The line selection criterion based on the fault power frequency quantity has the advantages that: because the line selection criterion is always established during the existence period of the fault, the line selection criterion has long duration and high reliability.
The grounding line selection criterion is used for comparing the reference quantity of the power frequency fault of the current on the load side of the transformer with the zero sequence current of the protected line, and the functional relation between the two current waveforms used for comparison is the comparison between the current and the current, and is basically not influenced by the distributed capacitance of the power system, so that the judgment result is less interfered and the reliability is very high.
Example IV
The purpose of this embodiment is to provide a small current grounding line selection method:
and judging whether the protected line is a faulty line or not by adopting a fault initial transient quantity method. The fault initial transient state quantity method uses the transient state quantity of the fault initial stage as the action criterion comparison quantity. The fault initial transient method can be used for grounding and line selection of a neutral point ungrounded system, and can also be used for grounding and line selection of a neutral point through arc suppression coil grounding system, and the neutral point through arc suppression coil grounding system shown in fig. 2 is used for analysis. At this time, the three-phase current on the load side of the transformer is represented as ia, ib, ic by instantaneous values; for zero-mode current of circuitInstantaneous value is denoted as i 01 、i 02 、i 03 。
When the power system operates normally, the circuit has no zero-mode current, and the load side of the transformer has no fault current. If the small-current grounding system has a grounding fault, the three-phase current on the load side of the transformer comprises the load current of the transformer and also comprises a fault quantity, wherein the fault quantity comprises a power frequency fault quantity and a transient fault quantity, and the three-phase current on the load side of the transformer is ia=iafh+Δia+δia, ib=ibfh+Δib+δib, ic=icfh+Δic+δic; wherein: iafh, ibfh, icfh the three-phase load currents Δia, Δib, Δic the three-phase power frequency fault currents δia, δib, δic the three-phase transient fault currents. The zero-mode current of the lines L1, L2 and L3 is a fault quantity, the fault quantity comprises a power frequency fault quantity and a transient fault quantity, and the fault quantity of the lines L1, L2 and L3 is expressed as delta i 01 ＝ΔI 01 +δ 01 、Δi 02 ＝ΔI 02 +δi 02 、Δi 03 ＝ΔI 03 +δi 03 ；ΔI 01 、ΔI 02 、ΔI 03 Representing the power frequency fault quantity, delta i 01 、δi 02 、δi 03 Representing the amount of transient faults. The capacitive current flowing into the earth is denoted as i c Capacitive current i c The transient fault quantity of (a) is expressed as delta i c 。
As can be seen from fig. 2, the arc suppression coil has a great blocking effect on the transient fault quantity of the pulse property, so that: δia= (δi) c )、δib＝(-0.5δi c )、δIc＝(-0.5δi c )。
The analysis method is the same as the embodiment, and is not redundant. Analysis showed that: the low-current ground fault reference quantity generating device extracts transient fault reference quantity (delta ia) with different faults from ia, ib and ic, and the transient fault reference quantity waveform is similar to the transient fault quantity waveform of a fault line in the opposite direction; the transient fault reference waveform is similar to the transient fault quantity waveform of the non-fault line in the same direction.
Therefore, the small-current grounding line selection device of the protected line can judge whether the line is faulty or not by comparing the small-current grounding line selection device with the transient fault reference transmitted by the small-current grounding fault reference generation device with the transient fault reference of the protected line.
It should be noted that the transient fault amount of the protected line is the transient fault amount of the zero-mode current of the protected line and the transient amount of the zero-mode current of the protected line.
The grounding line selection criterion is used for comparing the reference quantity of the transient fault of the current on the load side of the transformer with the transient fault quantity of the protected line, and the functional relation between the two current waveforms used for comparison is basically not influenced by the distributed capacitance of the power system, so that the judgment result is little in interference and high in reliability.
In this embodiment, the step of extracting the transient fault reference of the fault phase by the low-current ground fault reference generating device is as follows:
step (1) adding three-phase currents ia, ib and ic at the load side of the transformer to obtain three times of zero sequence current 3I 0 ＝(ia+ib+ic)；
Step (2) adding two non-fault phase currents at the load side of the transformer, namely (ib+ic);
step (3) filtering the transient fault quantity of the current obtained in the step (2) to obtain (Ib+ic);
step (4) adding the current obtained in the step (3) to the current ia of the fault phase on the load side of the transformer to obtain Ib+ic+ia;
and (5) subtracting the current obtained in the step (1) from the current obtained in the step (4), wherein the difference is the transient fault reference quantity (delta ia) of the fault phase, namely delta ia= (ib+ic) +ia- (ia+ib+ic) =ib-ib+ic-Ic.
The method for extracting transient fault reference quantity of the fault phase by the low-current ground fault reference quantity generating device can also be calculated by the following modes, and specifically comprises the following steps:
step (1) obtaining fault phase current of a load side of a transformer; for example: ia=iafh+Δia+δia;
step (2) duplicating the fault phase current of the load side of the transformer;
step (3) filtering the transient fault quantity of the current obtained in the step (2); obtaining Iafh+delta Ia;
step (4) subtracting the current obtained in step (3) from the current obtained in step (1), wherein the difference is the transient fault reference quantity (δia) of the fault phase, namely δia=ia- (iafh+Δia);
In this embodiment, the step of extracting the zero-mode current transient fault quantity of the protected line by the low-current grounding line selection device is as follows:
step (1) obtains the zero-mode current of the protected line, for example: the protected line is an L1 line, i.e. acquire i 01 ；
Step (2) copying the zero-mode current obtained in the step (1); namely: generating a current of the same magnitude and same waveform as in the first step;
step (3) filtering the power frequency fault quantity of the current obtained in the step (2) to obtain I 01 ；
Step (4) subtracting the current obtained in step (3) from the current obtained in step (1), wherein the difference is the transient fault quantity of the protected circuit, specifically, the transient fault quantity delta i of the protected circuit 01 ＝i 01 -I 01 。
If the transient fault quantity is to be extracted from the current containing the power frequency and the transient fault quantity, the traditional method is to directly filter the power frequency quantity in the current, and the rest is the transient fault quantity. The existing method for filtering the power frequency quantity adopts a power frequency trapper, and the existing power frequency trapper has unstable parameters, is easy to deviate and has poor filtering effect; the accuracy and reliability of the extracted transient fault amount are not high.
The method for extracting the transient fault quantity in the embodiment is as follows: establishing two identical currents containing power frequency and transient fault quantity, and filtering out the transient fault quantity of one of the currents, wherein the current only remains the power frequency quantity; the other current containing the power frequency and transient fault quantity is subtracted by the current of the residual power frequency quantity, and the difference value is the transient fault quantity needed by us. Experience has shown that: filtering the power frequency quantity in the current and keeping the transient fault quantity is difficult; but the transient fault quantity in the current is filtered, so that the power frequency quantity is easy to be reserved. Therefore, the present embodiment employs a "" desired, first-to-first "" approach. The removal from a current is what we want to get later. The more thorough the first removal, the more complete the later acquisition.
Particularly, the current at the load side of the transformer contains large power frequency load current, and the proportion of transient fault quantity is small. If the power frequency trapper is adopted to extract the transient fault quantity, the power frequency load current is slightly filtered out thoroughly, and the transient fault quantity is buried. The embodiment uses the power frequency load current of the non-fault phase at the load side of the transformer to eliminate the power frequency load current in the fault phase current, and the transient fault quantity in the fault phase current is easy to display.
The transient fault quantity has pulse property and high-frequency property, and has larger difference with the property of the power frequency quantity; the simplest method for filtering out the transient fault quantity of a certain current is as follows: a certain current is converted into a voltage waveform, a capacitor is used for filtering out high-frequency components in the voltage waveform, and power frequency components are reserved, so that the transient fault quantity of the current is filtered out greatly, and the power frequency quantity of the current is reserved greatly. The method for filtering out the transient fault quantity of a certain current can also be as follows: the current waveform is converted into digital quantity, a low-pass digital filter with cut-off frequency of 150Hz is applied to filter transient fault quantity in the current waveform, and power frequency components are reserved.
According to the step of calculating the transient fault quantity from the current transient value, the transient fault quantity can be integrated into a specific hardware circuit to realize; according to the method, a current transient fault quantity extraction circuit which is practical, simple and good in effect is shown in fig. 3. Fig. 3 includes three current transformers CT1, CT2 and CT3, the current transformer CT1 includes coils L1, L2, the current transformer CT2 includes coils L3, L4, and the current transformer CT3 includes coils L5, L6, L7; fig. 3 further includes an inductor L8, an amplifying circuit 1, and a transient fault handling circuit 2.
The synonym end of the coil L1 is connected with the homonym end of the coil L2; the homonymous end of the coil L3 is connected with the homonymous end of the coil L5, and the heteronymous end of the coil L2 is connected with the heteronymous end of the coil L5; the homonymous end of the coil L4 is connected with the inductor L8 in series and then is connected with the homonymous end of the coil L6, and the homonymous end of the coil L4 is connected with the homonymous end of the coil L5; two ends of the coil L6 are connected with two input ends of the amplifying circuit 1, and an output end of the amplifying circuit 1 is connected with an input end of the transient fault quantity processing circuit 2.
The working principle of fig. 3 is: the current (for example, ia) containing the power frequency and transient fault quantity flows into the homonymous end of the coil L1, flows through the coil L1 and the coil L3, and flows out of the heteronymous end of the coil L3; the coil L2 and the coil L4 respectively flow out currents, the magnitudes of the two currents are identical to the shape of the two currents, and the waveforms of the currents ia of the coils L1 and L3 are similar to those of the currents ia of the coils; the current transformer CT1 and the current transformer CT2 realize the function of the replica current ia. The current flowing out of the coil L2 is directly input into the coil L5; the current flowing out of the coil L4 is filtered by the inductor L8, so that the functions of retaining the power frequency component and filtering the high frequency component are realized; coil L2 and coil L4 flow two currents, one is not filtered and the other is filtered; one from the homonymous end of coil L5 and one from the heteronymous end of coil L6; the current transformer CT3 realizes the function of subtracting two currents in the coil L5 and the coil L6; the coil L7 flows out as the difference of the two currents, namely: transient fault amount current δia; the transient fault quantity current delta ia is too small, amplified by the amplifying circuit 1 and is input to the transient fault quantity processing circuit 2; the transient fault amount processing circuit 2 further processes the transient fault amount to obtain a suitable transient fault amount.
The transient fault amount current δia flowing out of the coil L7, if further contains a larger power frequency component, may be further designed into the transient fault amount processing circuit 2 to be a set of transient fault amount extraction circuits, which still use the above-mentioned step of calculating the transient fault amount from the current transient value.
The transient fault quantity extracted by the circuit can be a transient fault reference quantity of the fault phase, and can also be a zero-mode current transient fault quantity of a protected circuit.
The present embodiment adopts the "desired, first-to-last" method, which requires filtering out the transient fault amount of a certain current. The method for filtering the transient fault quantity of a certain current is numerous, a plurality of reserved power frequency components are accumulated in the circuit engineering for a long time, and experience and technology for filtering high-frequency components can be used for filtering the transient fault quantity by referring to the technology, so that the power frequency components are reserved. These are common knowledge and are not listed.
The method for extracting the transient fault quantity of the invention has simple process and higher accuracy and reliability. The extracted transient fault quantity relatively completely reserves the original transient fault quantity waveform before being extracted. A good foundation is laid for the correct judgment of the action criteria.
Compared with the prior art, the method for extracting the transient fault quantity of the line is simpler; the extracted transient fault quantity waveform relatively completely retains the original transient fault quantity waveform before being extracted.
Example five
The purpose of this embodiment is to provide a small current grounding line selection method: and judging whether the protected line is a faulty line or not by adopting a fault initial transient state quantity method and a power frequency fault quantity method at a neutral point through an arc suppression coil grounding system. The method solves the defect that the prior power frequency fault quantity method can only be used for a neutral point ungrounded system and cannot be used for a neutral point arc suppression coil grounding system. The analysis is carried out below, and the power frequency fault quantity method is used for realizing the neutral point through arc suppression coil grounding system.
As shown in fig. 2, when the neutral point fails through the arc suppression coil grounding system, the neutral point will inject inductive current into the ground through the arc suppression coil, and the power frequency of the inductive current is expressed as I due to the large interruption of transient fault quantity by the arc suppression coil L . Line L1 develops an a-phase earth fault and an inductive current I flows from the neutral point of the transformer through the arc suppression coil to ground L Flowing into phase a of the faulty line L1 from phase a of the faulty line will affect the zero sequence current magnitude and direction (I 01 ＝-I c -I L +k 1 I c ) Current (-I) c -I L ) Flows into the a-phase of the busbar M and then into the a-phase coil of the transformer, and affects the power frequency failure amount of the a-phase coil on the load side of the transformer (Δia=i c +I L ) Then flows into the neutral point of the transformer to form inductive current I L Is provided. Capacitive current I c The closed loop of (c) is described in the third embodiment, and is not further described.
It can be seen that the inductive current I L The magnitude and phase of the transformer load side fault phase fault current Δia are affected, but the magnitude and phase of the non-fault phase fault currents Δib and Δic are not affected.
When the low-current grounding system is in a fully compensated state, i.e. |I L ∣＝∣I c Negative sequence current component of fault phase of load side fault of transformer
I 2 ＝(Ia+a 2 Ib+aIc)/3
＝(ΔIa+a 2 ΔIb+aΔIc)/3
＝(0+a 2 ΔIb+aΔIb)/3
＝(-ΔIb)/3
Zero sequence current of load side of transformer:
I 0 ＝(Ia+Ib+Ic)/3
＝(ΔIa+ΔIb+ΔIc)/3
＝(0+ΔIb+ΔIb)/3
＝(2ΔIb)/3
it can be seen that if 2I 2 ∣＝∣I 0 And the system is in a fully compensated state.
When the power system is in a fully compensated state, the line zero sequence current (I 01 ＝-I c -I L +k 1 I c ＝k 1 I c ) The zero sequence current phase of the fault line is the same as that of the non-fault line; at this time, the low-current grounding line selection criterion based on the power frequency fault quantity cannot select a fault line. Therefore, the power frequency fault quantity method cannot be used for the complete compensation state.
When the low-current grounding system is in an under-compensated state, i.e., (|I) L ∣<∣I c I), the fault power frequency quantity delta ia=i of the fault phase of the load side of the transformer c +I L ＝(1-K Q )I c Wherein: k (K) Q Is a proportionality coefficient; when arc suppression coil current I L K when changing between 0 and 1 Q ＝0～1。
Negative sequence current of the fault phase:
I 2 ＝(Ia+a 2 Ib+aIc)/3
＝(ΔIa+a 2 ΔIb+aΔIc)/3
＝((1-K Q )I c +a 2 (-0.5I c )+a(-0.5I c ))/3
＝(ΔIa+a 2 (-0.5ΔIa)+a(-0.5ΔIa))/3
＝(0.5-K Q /3)I c
and has zero sequence current:
I 0 ＝(Ia+Ib+Ic)/3
＝(ΔIa+ΔIb+ΔIc)/3
＝((1-K Q )I c +(-0.5I c )+(-0.5I c ))/3
＝(ΔIa+a 2 (-0.5ΔIa)+a(-0.5ΔIa))/3
＝(-K Q /3)I c
I c ＝2(I 2 -I 0 )
therefore, when the low-current grounding system is in an under-compensation state, the power frequency fault reference quantity I 2 The phase of (c) is not changed.
If (|I) L ∣<∣-I c +k 1 I c I), then the fault line zero sequence current (I 01 ＝-I c -I L +k 1 I c ＝k 1 I c ) The phase of (c) does not change. At this time, the fault reference quantity is opposite to the zero sequence current of the fault line; the fault reference is in the same direction as the zero sequence current of the non-fault line. "still correct". The power frequency fault amount can be used to determine whether the protected line is a faulty line. It can be seen that as the arc suppression coil current increases, the reliability gradually decreases; when |I L ∣＝∣-I c +k 1 I c And if so, judging whether the protected line is a faulty line or not by adopting a power frequency fault quantity method.
To ensure |I L ∣<∣-I c +k 1 I c The |2I criterion is satisfied 2 ∣>∣K set I 0 -wherein: k (K) set And 1-5 is taken as a reliable coefficient, and is selected according to operation experience.
Applying criteria (|2I) 2 ∣>∣K set I 0 And) so that the power frequency fault quantity method of small current grounding line selection can be used for a part of the under-compensation state of the neutral point through the arc suppression coil grounding system The ground line selection reliability of the scene is improved.
The low-current grounding system is in an overcompensated state, i.e., (|I) L ∣>∣I c |) or (|2I) 2 ∣<∣I 0 -). The overcompensation state does not allow the adoption of a power frequency fault quantity method to judge whether a protected line is a faulty line or not, which is common knowledge. No more encumbrance is required.
When the power system is operating normally, the three-phase load may be unbalanced. The negative sequence component of the unbalanced three-phase current has adverse effect on the power frequency fault quantity line selection criterion of the low-current grounding line selection of the invention, but does not affect the fault initial transient quantity method line selection criterion of the low-current grounding line selection of the invention. Therefore, when the power system normally operates, the small-current grounding fault reference quantity generating device can detect whether the load current has a certain negative sequence component, if so, an alarm signal is sent out to inform operators on duty to process, and meanwhile, the power frequency fault quantity line selection criterion of the small-current grounding line selection is blocked, and the fault initial transient quantity method line selection criterion of the small-current grounding line selection is opened.
While the foregoing description of the embodiments of the present invention has been presented in conjunction with the drawings, it should be understood that it is not intended to limit the scope of the invention, but rather, it is intended to cover all modifications or variations within the scope of the invention as defined by the claims of the present invention.
Claims (13)
1. The low-current grounding line selection method is characterized by comprising the following steps of:
establishing a power frequency fault reference quantity based on the three-phase current instantaneous value of the load side of the transformer;
calculating the zero sequence current of the protected line based on the zero mode current instantaneous value of the protected line;
comparing the zero sequence current of the protected circuit with a power frequency fault reference quantity, and if the power frequency fault reference quantity is opposite to the zero sequence current of the protected circuit, determining that the circuit is a fault circuit; if the power frequency fault reference quantity is the same as the zero sequence current direction of the protected circuit, the circuit is a non-fault circuit.
2. The small current grounding line selection method as claimed in claim 1, wherein when the power frequency fault reference is established based on the instantaneous value of the three-phase current at the load side of the transformer, the negative sequence current of the fault phase at the load side of the transformer is used as the power frequency fault reference.
3. The small current grounding line selection method as claimed in claim 1, wherein a power frequency fault quantity method of small current grounding line selection is used for a scene of an under-compensation state of a neutral point through an arc suppression coil grounding system by using a criterion, wherein the criterion is as follows:
∣2I 2 ∣>∣K set I 0 i, wherein I 2 For the negative sequence component of the fault phase of the load side of the transformer, I 0 K is zero sequence current of load side of transformer set The reliability coefficient is 1-5.
4. The low-current grounding line selection method is characterized by comprising the following steps of:
establishing transient fault reference quantity based on the three-phase current transient value of the load side of the transformer;
calculating the transient state quantity of the zero-mode current of the protected line based on the transient value of the zero-mode current of the protected line;
comparing the transient state quantity of the zero-mode current of the protected circuit with a transient state fault reference quantity, and if the waveform of the transient state fault reference quantity is similar to the waveform of the transient state quantity of the zero-mode current of the protected circuit in the opposite direction, determining that the circuit is a fault circuit; if the waveform of the transient fault reference quantity is similar to the transient quantity of the zero-mode current of the protected line in the same direction, the line is a non-fault line.
5. The method for selecting a low-current ground line according to claim 4, wherein the step of establishing the transient fault reference based on the transient values of the three-phase current on the load side of the transformer comprises the steps of:
adding three-phase currents at the load side of the transformer to obtain a first current;
adding the two non-fault phase currents on the load side of the transformer;
filtering transient fault quantity of current obtained by adding two non-fault phase currents;
adding the current obtained after the transient fault quantity is filtered with the fault phase current of the load side of the transformer to obtain a second current;
And subtracting the first current from the second current, wherein the difference value is the transient fault reference quantity of the fault phase.
6. The method for selecting a low-current ground line according to claim 4, wherein the step of establishing the transient fault reference based on the transient values of the three-phase current on the load side of the transformer comprises the steps of:
step (1) obtaining the current of the same fault at the load side of the transformer;
step (2) copying the current obtained in the step (1);
filtering transient fault quantity of the current obtained by replication;
and (4) subtracting the current obtained in the step (3) from the current obtained in the step (1), wherein the difference value is the transient fault reference quantity of the fault phase.
7. The method for small current grounding line selection as recited in claim 4, wherein the step of calculating the transient of the zero mode current of the protected line comprises the steps of:
step (1) obtaining zero-mode current of a protected circuit;
step (2) copying the zero-mode current obtained in the step (1);
filtering the transient fault quantity of the zero-mode current obtained by replication;
and (4) subtracting the current obtained in the step (3) from the zero-mode current obtained in the step (1), wherein the difference value is the transient state quantity of the zero-mode current of the protected line.
8. A low-current grounding line selection system, which adopts the low-current grounding line selection method as set forth in any one of claims 1 to 7, and is characterized by comprising:
At least one reference quantity generating device for low-current grounding faults and at least one low-current grounding line selecting device;
all the low-current grounding line selection devices are communicated with one low-current grounding fault reference quantity generation device;
the low-current ground fault reference amount generating device is configured to: when a small-current ground fault occurs, establishing a small-current ground fault reference quantity based on a three-phase current instantaneous value at the load side of the transformer;
the low current ground line selection device is configured to: when a small-current ground fault occurs, calculating the transient quantity of the zero sequence current or zero mode current of the protected line based on the zero mode current transient value of the protected line; and comparing the transient state quantity of the zero sequence current or zero mode current of the protected circuit with the corresponding small current grounding fault reference quantity, and judging whether the circuit is a fault circuit.
9. The low current ground fault reference amount generating device of claim 8, wherein the number of low current ground fault reference amount generating devices is equal to the number of low current ground fault line selecting devices, or the number of low current ground fault reference amount generating devices is less than the number of low current ground fault line selecting devices.
10. The small current ground fault line selection system as claimed in claim 8, wherein said small current ground fault reference amount generating means sends the generated small current ground fault reference amount to at least one of said small current ground fault line selection means;
The small-current ground fault reference quantity generating device and the small-current ground line selecting device are equal in quantity or unequal in quantity for information interaction.
11. The small current grounding wire selection system as claimed in claim 8, wherein said small current grounding fault reference amount generating means further receives a bus three-phase voltage, judges whether a small current grounding fault occurs based on the bus three-phase voltage, and judges the fault phase.
12. The small current grounding wire selection system of claim 8, further comprising a current/voltage converter which converts a three-phase current instantaneous value on a load side of the transformer into a voltage wave of a similar waveform, and transmits the converted voltage wave to said small current grounding fault reference amount generating means.
13. The small current grounding line selection system as claimed in claim 8, wherein said small current grounding fault reference generation means and said small current grounding line selection means each include a current transient fault amount extraction circuit for calculating a transient amount of zero mode current of a protected line or a transient fault reference of a fault phase from a current transient value, said circuit comprising: current transformers CT1, CT2 and CT3;
The current transformer CT1 comprises coils L1 and L2, the current transformer CT2 comprises coils L3 and L4, and the current transformer CT3 comprises coils L5, L6 and L7;
and an inductor L8, an amplifying circuit, and a transient fault amount processing circuit;
the synonym end of the coil L1 is connected with the homonym end of the coil L2;
the homonymous end of the coil L3 is connected with the homonymous end of the coil L5, and the heteronymous end of the coil L2 is connected with the heteronymous end of the coil L5;
the homonymous end of the coil L4 is connected with the inductor L8 in series and then is connected with the homonymous end of the coil L6, and the homonymous end of the coil L4 is connected with the homonymous end of the coil L5; the two ends of the coil L6 are connected with the two input ends of the amplifying circuit, and the output end of the amplifying circuit is connected with the input end of the transient fault quantity processing circuit.
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